Guten Tag from Germany. My first post so hallo to all.

I am a brit, been in the fatherland now for 20 years. I ride trials bikes ancient and modern and have quite a few...300Gasgas, 270 Beta...but lots of twin shock fantics. I am not a complete dumbboy with a set of tools so, can do most things , including (trials bike) engine rebuilds.

I just bought a 426 YZF 2003 and want to do the right things before gettin serious with in. Its had regulat oil changes etc but the history is not really known, so....

I intend to change the oil, filter, check brakes, head, wheel and linkage bearings etc etc. I also will check and adjust the valve shimming as a mater of course.

My question is, do I need to strip it straight away to be on the safeside. Assuming the valve clearances are ok, or not far off and can be adjusted, what else NEEDS doing. Camchain? Piston? Headoff and new Valves?

I will only be having fun and not racing but what do you guys recommend? I dont want the piston breaking up...if it was a 125 2stroke I probably would do the piston anyway. Do I need to do it on the 426?

Your thoughts appreciated


Welcome to TT.

There's a YZ400/426/450 section, you should post your questions there for best results.

Are you sure it's a 426? '03 was the first year for the 450.

Is the oil dipstick at the top of the frame between the gas tank and the upper triple clamp, or down on the engine?

Does it have a four or five speed trans?

Is there a decompression lever or can you just kick it to start it?

I would do all the things you mentioned, then ride it to see what you have.

Ok, without a full history, there are several ways to tell a few things right off the bat.

General shape of the bike tends to give you an indication of how hard it has been ridden and whether it's got low or high hours.

Does the Cylinder look sand blasted? - if so - it's got a replated cylinder in it - in which case - that AND the piston were likely done at least once.

When you check your valve clearances, it will be worthwhile to pull the cams and flywheel and replace the cam chain - for the 35 it costs, it's cheap reassurance against it breaking and your whole motor going with it. At the same time - since you have access to the shims, check the shim sizes that are lazer etched onto the shims - this will give you an indication of where in their service life the valves are at since stock shims tend to be within a small range of sizes (check your manual).

When replacing the cam chain - check the gear on the crank for wear.

Looks like a pretty good deal. It may be an '01, it looks like it has the '01 and earlier style swing arm. It may have been replaced too, so who knows. It's definitely a 426 though.

I agree. The subframe is steel so it's not a 450f.. probably a 2001 or 2002 426f. Looks like a nice ride. I would remove cam cover and check valve clearance. I would remove head and inspect how the valve seats seal with brake cleaner. Inspect cam chain and cam chain tensioner. I would remove the block to inspect the piston and rings (and replace with wiseco standard kit if not in the specs). Build it back from there. I don't like high compression pistons cause they cause generation of quite a lot of additional heat. Consider hot cams stage 1. Not necessary because these bikes generate lots of torque and hp.. more than you can probably handle. But if you are a power freak... it is cool. As you build it back, put a new NGK irridium plug. I would definitely check the clutch lever position... looks quite a bit down. Bring it back up a bit. Consider buying hand guards... Ride and have fun ! :-)

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